- Teacher Guide
- Student activity, Graph Type A, Level 2
- Student activity, Graph Type B, Level 2
- Student activity, Graph Type C, Level 2
- Grading Rubric
Imagine walking through a deciduous forest in the middle of summer. You can hear birds chirping, a slight breeze rustling the leaves, and a faint pinging noise like rain. However, what you hear is not rain – it is the sound of millions of forest insects defecating!
Forest insects, like caterpillars, are a great source of food for many species. As such, caterpillars have many defense strategies to protect themselves and evade predators, including camouflage to avoid detection, nasty defensive chemicals and bright colors to warn predators to stay away, or even building shelters out of plant leaves to hide in. The smell of frass (insect poop) alerts predators that a tasty insect is in the area, so usually insects keep moving and leave their frass behind. But what if the insect relies on a shelter for protection and cannot keep moving away from its home?
The forest insect, Epargyreus clarus (the silver-spotted skipper) has a variety of defense strategies against enemies, including building leaf shelters for protection. While raising E. clarus caterpillars in the lab, a scientist noticed that E. clarus made a pinging noise in their containers. Upon further observation, it was discovered that they “shoot their poop”, sometimes launching their frass over 1.5m! The scientist wanted to determine why these caterpillars might engage in this very strange behavior. Perhaps flinging their poop is a defensive strategy to avoid predator detection.
To evaluate whether the smell of frass alerts predators to the presence of a caterpillar, the scientist Weiss conducted an experiment with the predatory wasp Polistes fuscatus. She allowed two E. clarus larvae to build shelters on a leaf and then carefully removed the larvae. She then inserted 6 frass pellets into one of the shelters, and 6 beads designed to look like frass but with no smell (control treatment) into the other. She placed the leaf in a cage containing an actively foraging wasp colony (n = 10 wasps), and recorded how many times the wasps visited each shelter (control or frass), and how much time the wasps spent exploring each shelter.
Additional teacher resources related to this Data Nugget include:
- A YouTube video of Epargyreus clarus “shooting its poop” (aka. ballistic defecation)
- The paper published using this data and testing alternative hypotheses: Weiss, M. R. (2003) Good housekeeping: why do shelter-dwelling caterpillars fling their frass? Ecology Letters 6(4): 361–370